Specifically, on this.
It’s a Voith Maxima locomotive which is the most powerful single engined diesel hydraulic model in the world. Sadly it turned out to be an answer to a question hardly anybody had asked and so production has ceased after only a couple of dozen being made.
Anyways, it’s a 3,600 kw or 4,800 bhp loco which can if so asked move 3,000 tonnes at up to 120 kmh or 75 mph.
So, how many gears does it need, given that heavy road going vehicles can have more than a dozen?